The security of blockchain has always been closely tied to its adoption within the industry. Unfortunately, security attacks on blockchain never cease to emerge--from early attacks such as 51% attack, Sybil attack, eclipse attack, and replay attack to modern attacks such as those leveraging security gaps of cryptocurrency exchanges, logical flaws of new cryptomining protocols, and the flash loan issues. This session explains the overall attack surface of blockchain with insights into hackers' tactics and techniques, while providing tips to prevent and remediate the loss of such attacks from different perspectives. The intended audience includes hackers who want to get rich overnight, the general public who wants to use blockchains safely, system administrators who want to get off work on time, and developers who want to design the best blcokchain trading protocols.